It is known to provide flat stroke conveyors. Such conveyors may be reciprocating conveyors only or a combination of a reciprocating conveyor and a rocking conveyor. It is further known to provide drives for such reciprocating conveyors which will produce the desired reciprocations of a work piece to effect reciprocation of the work piece relative to a blast wheel or wheels and to periodically rapidly return the conveyor so that the work pieces will retain their advanced positions and thus progressively move past the blast area of a blast wheel. However, such drive units are relatively large and relatively heavy and suitable primarily only for very large work pieces, such as engine blocks and the like. At the same time, however, such drives are very expensive.